Attack rolls for a D20 like system

The problems you describe:

> - Weak players cannot touch very strong creature
> - Strong players cannot miss
> - Better stats is not that significant

are not so much a result of the dicing system as of the advancement system and the D20 mindset over all. D&D and the many games it inspire offer a very particular type of gameplay:

1) Start very weak
2) Level up a bunch
3) Become ridiculously powerful relative to where you started

You will fight a losing battle if you try to use D20 systems for a different kind of gameplay. It's possible, but you'll have to do things like this:

> - The maximum probability to his is always 80%, and the minimum probability to hit is always 20%.

to offset conventions like this:

> The attacker use his attribute (1-20) as his "combat skill" + 1D20 + his level.

If you picture the graph of your "to hit" system, it will contain lots of sharp edges where you impose limits like "minimum chance to hit is always 20%." You'll feel these edges in odd places, like low level characters learning that level doesn't matter against tough opponents, but makes a huge difference against weaker ones, or high level characters finding that there's no difference between kobolds and ogres.

In the end, you can't have it both ways: level either makes an appreciable contribution to combat, or it doesn't. If it does, leveling up will eventually make you incredibly powerful. That's not a bad thing, but if it's not what you want, build level out of your to-hit math.

There are excellent alternatives to D20 out there (see the Hero System, for example), that are better at modeling gradual increases in power as players earn experience. Maybe you'll have more success implementing models like those to get the gameplay you want.

I've been reading the posts about your RPG-in-the-making and think it sounds neat. I'd love to hear what kind of gameplay you want and brainstorm mathematical models that create that gameplay. It may be that starting with D20 won't get you what you're after.

Good luck!

I loved Wizardry, and it's great that your remember it and want to make something inspired by it -- but it's gameplay was almost exclusively about leveling up. If you downplay the effect of leveling, you are making a different game.

In your original post, one of the problems you identified was "stats don't make much difference." So, why not start there, and have stats, rather than level, be the basis of your combat formula. You could give players a small stat bonus per level (maybe even based on class), but you could cap it or make the bonus diminish with increasing level. Something like:

Combat Skill = Dexterity / Encumbrance

Where encumbrance is always 1 or greater.

So

Required Hit Roll = 10 - Attacker's combat skill + defender's combat skill

If you stick with Wizardry's 3-18 stat range, it's still possible to get 100% chance to hit with this formula. If you dislike that, you could modify it as follows:

Chance to hit = 10.5 - (Attacker's combat skill - Defender's combat skill) * 2 / 3, and round in favor of the person with the lower stat.

So that an attacker with 18 DEX vs a defender with 3 DEX only needs

10.5 - (18 - 3) * 2/3 = 10.5 - 15 * 2/3 = 0.5 which rounds in the defender's favor to 1,

And an attacker with 3 DEX vs a defender with 18 DEX needs

10.5 - (3 - 18) * 2/3 = 10.5 + 15 * 2/3 = 20.5 which rounds in favor of the attacker to 20.

Of course, encumbrance and stat bonuses could screw this up, changing the range of possible skill ratios to be outside [1/6, 6]. Also, it's not ideal if you convert to a tabletop RPG.

Another way to deal with the problem of vastly different skills is to increase combat skill non-linearly with the stats involved. For example, make a chart like this:

ATTACKER DEX > DEFENDER DEX
=====================
Attacker Dex / Defender Dex >= 1 and < 2--hit roll: 10+
Attacker Dex / Defender Dex >= 2 and < 3--hit roll: 9+
Attacker Dex / Defender Dex >= 3 and < 4--hit roll: 8+
Attacker Dex / Defender Dex >=4 and < 5 --hit roll: 7+
Attacker Dex / Defender Dex >=5 and < 6 --hit roll: 6+
Attacker Dex / Defender Dex >=6 and < 7 --hit roll: 5+
Attacker Dex / Defender Dex >=7 and <8 --hit roll: 4+
Attacker Dex / Defender Dex >=8 and <9 --hit roll: 3+
Attacker Dex / Defender Dex >=9 ------------hit roll: 2+

DEFENDER DEX < ATTACKER DEX
=====================
Defender Dex / Attacker Dex >= 1 and < 2--hit roll: 11+
Defender Dex / Attacker Dex >= 3 and < 4--hit roll: 13+
Defender Dex / Attacker Dex >= 4 and < 5--hit roll: 15+
Defender Dex / Attacker Dex >= 5 and < 6--hit roll: 17+
Defender Dex / Attacker Dex >= 6 and < 7--hit roll: 19+
Defender Dex / Attacker Dex >= 7 ------------hit roll: 20+

With a system like this, you can be more liberal about giving stat bonuses with items.

Consider a DEX 12 cleric attacking a DEX 15 thief. The defender has a higher DEX, so you use the second chart. The stat ratio is 15 / 12 = 5 / 4 which is greater than 1 but less than 2, so the cleric needs an 11+ to hit. Conversely, the thief only needs a 10+ to hit the cleric, so his DEX gives a slight advantage.

Now assume you included encumbrance. Maybe the cleric wears chain mail that reduces his effective DEX to 5. Now the ratio is 15 / 5 = 3 in the thief's favor, which requires the cleric to roll 13+. Meanwhile, the thief needs only 8+, giving him a 25% advantage. Note that in this system, armor reduces incoming damage, rather than increasing the hit requirement.

Now imagine the cleric goes up against a blink dog with an effective DEX of 25. The ratio becomes 25 / 5 in the dog's favor, meaning the cleric needs 17+ and the dog only 6+.

As the cleric advances in his career, he finds loot which includes these items:

Boots of Agility: +15 DEX
Ring of Speed: +5 DEX
Hermes' Blood (potion bestowing a permanent +6 DEX)
Limited Wish (which he used to increase his DEX by 3)
Magic Chain Mail (+3 DEX and no encumbrance penalty)

The cleric's DEX is now: 12 + 15 + 5 + 6 + 3 + 3 + 3 = 47

He once again runs up against blink dogs, only now, he has the advantage with a ratio of 47 / 25 which is slightly less than 2. He needs a 9+ to hit, and the blink dogs need 11+.

Now, these numbers may not be to your liking, but consider the system as a whole. The cleric would have had to play for a *long* time to get those items, and he can look at them and see tangible benefits ("Oooo! +5 DEX! Awesome!"). And he feels the difference when he revisits old monsters...BUT...the monsters are still a threat, hits aren't automatic, and combat remains interesting.

Of course, you could still use level as the main combat stat and scale it non-linearly, but that has some issues. First, players expect to have a limited inventory, so if you tie stat increases to inventory items, there is a natural mechanism to cap how many bonuses a player can stack. Players expect level to go up to 50 at least -- and then they expect expansions to raise the cap. Also, players have been taught that level makes an *overwhelming* difference to combat. If you go that direction, you run the risk of disappointing your core audience.

You have a lot of options, and your complaints about the D20 system are on target. Math is rich with possibilities to address them, but most of the solutions depend on breaking away from D20 assumptions.

I saw that, I think. Is this the formula you mean:
> The attacker use his attribute (1-20) as his "combat skill" + 1D20 + his level.

The difficulty is that it still includes the level. It's exactly what you pointed out: if you include the level at all, eventually, the player becomes un-hittable. By using *just* the attribute and leaving level out of it, you reduce this problem.

As for the rest of my "wall of text" (sorry about that), it's a big departure from normal D20 math, so it probably won't suit your needs. :(

The Hero system works the same way. Stats and abilities instead of level makes for a very different, but equally viable, type of game.

I understand what you're going for better, now.

I'm somewhat confused why you say one system is harder to implement than the other, since they are pretty much mathematically equivalent. In one case, you add the level to the base multi-hit and cap the result. In the other, you add the level directly to the combat skill and cap the level, but it's the same:

Combat skill - (base-multi-hit - level) <-- capped - weapon multi-hit
vs
Combat skill + level <--capped - base multi-hit - weapon multi-hit

As far as implementation goes, it doesn't seem like there are any more variables, and in any case, 1 or two more variables doesn't significantly increase the development cost in a variable-heavy game like an RPG.

If you've already chosen a system with linear progression which includes level in the to-hit roll, your fate is set. Your game is going to feel like a D20 system within some level range. Wherever you cap the numbers, it's going to feel like progression stops -- because it does.

Good luck with your solution and the game. I hope you you enjoy the development experience more this time around.